At the 2008 Conference in Arusha Tanzania, the Technical and Operations Committee (TOC) presented a working paper on a new separation standard being developed through ICAO Separation and Airspace Safety Panel (SASP). This working paper detailed the panel work that had been done so far – but was inconclusive due to the work not being finalised in SASP. This working paper provides an update on the work completed thus far and discusses the concerns that have been raised in SASP – with particular emphasis on the areas that are of concern to IFATCA.

TOC believes that there is insufficient global support for managing ‘incorrect FlightId’ and proposes policy to correct this. TOC also believes that globally, the issue of incorrect FlightId warrants further investigation.

1.1  In Arusha (Tanzania), the IFATCA Technical Operations Committee (TOC) presented a working paper on the developments of ADS-B In Trail Procedures (ADS-B ITP). It was determined that due to the immaturity of the work and the need to follow this closely, TOC would continue to monitor and report on the work being completed.

1.2  Since Arusha there have been many activities completed with ITP. This has included the following:

1. Radio Technical Commission for Aeronautics (RTCA)/ European Organisation for Civil Aviation Equipment (EUROCAE) Special Committee (SC)-186 – Approval of the Requirements Focus Group (RFG) “Safety, Performance and Interoperability Requirements Document for Air Traffic situational Awareness- In Trail Procedures (ATSA-ITP)” – This document contains an Operational and Service Environment Description (OSED), an Operational and Performance Assessment (OPA) and an Operational Safety Assessment (OSA).
2. Australia has published the results of a joint Airservices Australia/ National Aeronautics and Space Administration (NASA) ITP controller experiment.
3. Co-operative Validation of Surveillance Techniques and Applications of ADS-B (CRISTAL)-ITP program has conducted simulations and a live flight trial of ADS-B ITP.

These activities have been used by the International Civil Aviation Organisation (ICAO) Separation Airspace Safety Panel (SASP) to progress the work forward. SASP have split the work into two areas, these are – mathematicians doing the collision risk modelling and a working group developing the procedures and Procedure of Air Navigation (PANS) Air Traffic Management (ATM) amendments.

2.1 A revisit of the concept

2.1.1  ADS-B ITP is the process whereby Global Navigation Satellite Systems (GNSS) and ADS-B data is used to apply distance based longitudinal separation.

2.1.2  GNSS is an autonomous geo-spatial positioning system with almost global coverage. GNSS allows electronic receivers to determine their location (longitude, latitude, and altitude) to within a few metres using time signals transmitted along a line of sight by radio from satellites.

2.1.3  ADS-B is a function on an aircraft or surface vehicle that periodically broadcasts its state vector (horizontal and vertical position, horizontal and vertical velocity etc, as determined from the GNSS) and other information. ADS-B cannot function without a system to provide this information – Current ‘ICAO Annex 10’ approved ADS-B systems need GNSS to provide the data so it can broadcast this for reception by both airborne and ground receivers.

2.1.4  For the proposed ADS-B ITP, the manoeuvring aircraft (in this case could be trailing or leading) obtains the relevant ADS-B data, including Flight Identification (Flight ID), altitude, and ground speed from the non-manoeuvring (leading or trailing) aircraft.

2.2.2  IFATCA strongly believes that while ADS-B ITP is categorised within the work package of ‘ATSA’, it is important to clearly state that it is not a ‘situational awareness’ tool and not a ‘delegation of separation’ – but a separation standard to be applied with similarities to a conventional DME standard.

2.2.3  ATSA-ITP SPR RTCA/DO-312 was approved on June the 19th 2008.

2.3 ICAO

2.3.1  Since conference the SASP has continued it’s work on ADS-B ITP. The IFATCA representative has presented items at the last two meetings and has since detailed the work completed in his latest report. This information will be used substantially in this working paper.

2.3.2  SASP Meeting Reports WG/WHL/13/14

While TOC has strived to capture the changes from both meetings – TOC has determined that to ease confusion and to provide continuity for the reader we will only capture the changes as a whole. This will allow us to report the finalised work of the last two meetings.

2.3.2.1 Review of Project Team Six (PT-6) report (SASP/WG/WHL/13 PT-6 Report Appendix E)

Australia presented the final developments of the ATC simulator trials held in Melbourne. These included the following observations:

• ITP was considered as being little different to a DME go through manoeuvre, or use of Automatic Dependence Surveillance – Contract (ADS-C) information for separation.
• ITP represents a shift in workload rather than an increase. [TOC Comment– ATC involved in the trials believed that using ADS-B ITP at times when normal restrictions would not have allowed a level changed – created a shift in workload, as the result of these level changes removed typical ‘workload related’ scenarios normally experienced later in the flight]
• While the pilot re-check is a fundamental change in application of a separation standard, it may serve to overcome some of the limitations associated with the provisions of standards using HF communications.
• Use of VHF communications with ADS-B ITP and third party callsign use, were not seen as a problem. Several participants considered that any problems are likely to be overcome with training and experience.
• Some concerns were raised how the ITP procedures were written and taught. With initiation criteria, rather than minimum separation distance, controllers were not actually aware of the standard they were protecting. It was also noted that, as it stands today, for a potential separation breakdown the first thing a controller does is pass traffic – with ITP this has technically already been done.

The following issues were also noted:

• HF was not simulated
• Most pilots do not recognise other airlines ICAO three letter identifier as they typically do not see them on their Traffic Collision and Avoidance System (TCAS) type displays.

2.3.2.2 The project team then went on to discuss the live ITP simulation in Reykjavik (surveillance) airspace. These trials were conducted under the auspices of CRISTAL ATSA-ITP project.

The CRISTAL ITP validation exercises consisted of the following:

• A set of real time experiments conducted at Airbus in Toulouse, National Air Traffic Services (NATS) – UK premises in Prestwick and the Icelandic Air Navigation Service provider (ISAVIA) premises in Reykjavik. The real time experiments consisted of operational evaluations of In Trail Procedure application supported by ADS-B information in the cockpit, from a pilot and pilot/controller cooperation perspectives.
• A benefit analysis conducted by NATS team based on real traffic sample over North Atlantic area and the expected growth of ADS-B out traffic for 2010/2015/2020.
• A flight test within Reykjavik FIR conducted in cooperation with Airbus, ISAVIA, NATS, Alticode and Scandinavian Airlines (SAS). This live test consists of ITP manoeuvres in real operational context using airline aircraft as reference.

The conclusions from this trial were similar to those from the Melbourne simulator trials. The following is the summaries of discussion by PT-6 on the conclusions from the CRISTAL trials.

2.3.3.3  Specify Controller Pilot Data Link Communication (CPDLC) as required communication

One of the main reasons for promoting CPDLC as the sole means of communicating the ITP was the use of the reference aircraft call sign on the open frequency. Using radio callsigns is so interwoven in the radio procedures that ATC found it difficult to remember the phonetic format (QFA 25 – Quebec –Foxtrot – Alpha –Two –Five) for ITP use. It was also noted that controllers preferred CPDLC to ensure accuracy and clarity for instructions and ITP criteria. PT-6 discussed this but came to the conclusion that it would not mandate CPDLC use only- but that if States were to conduct their own safety assessment VHF communication could be used. It was agreed that ICAO would promote CPDLC as the preferred method and agreed that third party communications should not be endorsed in the PANS-ATM amendment.

2.3.3.4  Designation of the relative position of ITP aircraft vs. Reference aircraft

It was recommended that to use the terms “AHEAD OF/BEHIND” rather than “LEADING/FOLLOWING” in ITP communication (when specifying the relative positions of the ITP aircraft vs. reference aircraft).

2.3.3.13 Other issues considered (ITP discussions at SASP WG/WHL/14)

1. “either the ITP or reference aircraft can be ahead”.
2. Addition of ‘shall’ statements.
3. “ITP distance” will need to be clarified with clear illustrations to clarify that it refers to the difference between distances to a common point, not necessarily the distance between the ITP and the reference aircraft.
4. Diagram titles were corrected to include terminology ‘AHEAD OF’ and ‘BEHIND’ for consistency with phraseology and data link text.
5. It was emphasized that only ‘current’ track of reference aircraft is known to the ITP aircraft
6. Aircraft and the Air Operator must be appropriately approved for ITP. Discussion ensued regarding this point as to who which Panel/Working Group should initiate the preparation of the regulatory material used for certification of aircraft and approval of air operators. It was suggested that perhaps the Ops Panel or the ASP would be more qualified to lead this initiative.
7. It was again emphasized that when a requested ITP flight level is not available, the pilot shall be advised, and subsequently informed that another flight level might be available; the phraseology was amended as follows:
   (ITP Aircraft identification), REQUESTED LEVEL IS NOT AVAILABLE, ADVISE IF ABLE I-T-P (alternate flight level).
8. Definition of ITP equipment: All avionics which perform functions needed to support or perform the ADS-B In Trail Procedure. (Note: aircraft involved in development of ADS-B ITP were equipped with graphic displays for Cockpit Display of Traffic Information (CDTI))
9. The following definition of ITP criteria was included:
   ITP criteria: A set of conditions that must be satisfied prior to initiating or executing an ITP clearance
10. When finalizing the collision risk calculations the MSG concluded that changes needed to be made to the ITP initiation criteria to satisfy the Target Level of Safety (TLS) of 5×10-9 fatal accidents per flight hour. Further discussion indicated that the best means to achieve this was to change the original 3000ft vertical criteria between the ITP aircraft and reference aircraft to 2000ft. Once this change was made the conclusion was that the ITP procedure satisfied the TLS given the various assumptions that were made regarding the frequency of use etc.

2.4 ADS-B Use

2.4.1 In the working paper presented in Arusha, TOC discussed the issues associated with ADS-B transmitted data. While TOC has no intention of repeating the issues and views expressed in that working paper, the issue of how the aircraft will know what integrity values to use and how this will be filtered (if the value is less than required for use with this procedure) is of interest. This should be transparent to ATC, but for the pilot using this data the process is of significant importance. Comments received as part of the RFG Final Review And Comment (FRAC) process included concerns as to the amount of pilot knowledge required. It was determined that it should not be a ‘green-light’ approach but that the information displayed to the pilot must include those elements needed for correct pilot assessment.

2.4.2  One concern that TOC has is similar to that of the single emergency code management issue (detailed in working paper B.5.5/WP89 from Arusha) and for which IFATCA now has Policy. The guidelines for using ADS-B technology with known limitations are not globally managed. This ongoing issue is important for IFATCA as any pattern of State managed work-arounds (or airline managed) for ADS-B use is against the ‘globally harmonised’ and seamless Air Traffic Management (ATM) vision for the future. IFATCA would like to see a global approach to the management of any future use of ADS-B and datalink.

2.4.3  In Australia and Europe monitoring of incorrect FlightID input has shown inconsistent application. Incorrect Flight ID will also become a significant issue for the pilot, as the request for ITP includes assessment of this data. The question also remains on how ATC rectify this situation, do they ask for clarification, do they ask the pilot of the aircraft with the incorrect Flight ID to change it and broadcast the correct data – or does this become too complex? Or should ATC just reject the request? It is obvious that IFATCA would like to see these questions answered.

2.5 IFALPA

2.5.1 IFALPA (through ALPA) commented heavily in the FRAC process and have been monitoring the work of SASP. While not yet having policy on the use of ITP – they are aware of the potential issues and are monitoring closely.

2.6 IFATCA Policy

2.6.1 IFATCA has not yet developed policy on ADS-B ITP.

2.7 ADS-B ITP – Issues

2.7.1  The ADS-B ITP standard is being created to enable a new distance separation standard for the controller to use, especially in oceanic areas where large procedural standards currently apply. It is comparable to a DME distance standard – however it is a pilot using ADS-B information who is determining the distance from another aircraft (instead of the pilot reporting distance from a DME station or a waypoint). The controller is still responsible for separation. Simulations and trials of ADS-B ITP have been conducted in Australia, UK and Iceland and the oceanic controllers involved have indicated it is a useful standard and relatively simple to use (depending to some degree on the sophistication of the Flight Data Processing System that supports the controller). It is therefore appropriate for IFATCA to support the continued development of this standard. There are however issues that still need to be addressed which are the subject of continuing work in ICAO (SASP) and in other organisations.

2.7.2  The creation of the ADS-B ITP separation standard for the controller to use was seen as being easier and quicker than developing a new separation standard for pilot use (that is not addressing for now many issues associated with delegation of separation from the controller to the pilot). At the 2008 IFATCA annual Conference TOC presented a working paper introducing ADS-B ITP (B.5.4 WP88). In this working paper TOC discussed the issues of ITP being used as a ‘separation standard’ not as a ‘delegation of separation’. TOC has continued discussing this issue but recognises that IFATCA should support ICAO development of the ADS-B ITP standard, whilst of course ensuring that all aspects are addressed to ensure that it will be safe and practical for the controllers (and pilots) to use.

3.1  SASP has completed the ICAO Doc 4444 PANS–ATM amendment and is finalising the circular. The circular will contain important information in understanding and implementing the standard. The PANS-ATM amendment will need to obtain the full approval from ICAO (including review by the States) and so some changes are expected. IFATCA should participate in this review process.

3.2  RTCA has published ATSA-ITP Safety, Performance and Interoperability Requirements Document for ITP RTCA/DO-312.

3.3  Significant change due to CRM by the Maths Sub-group of SASP has reduced the original 3000ft vertical criteria from the ITP aircraft to any reference aircraft to 2000ft.

3.4  ADS-B/Datalink use needs to be globally harmonised – especially when new procedures are developed.

3.5  The line between a ‘delegation’ and a ‘separation standard’ has been blurred and needs to be monitored closely.

3.6  Significant work is required to correctly identify the training needs and education required both from a human factors standpoint and an operational need.

3.7  SASP believes that the issue of misidentification due to incorrect FlightID has been sufficiently addressed by the proposed amendment to ICAO Doc 4444 PANS-ATM. Nevertheless TOC has concerns that the responsibility to manage this misidentification becomes the responsibility of the controller. Experience with Mode S has shown many occurrences of incorrect FlightID and IFATCA believes that guidance relating to the management of this problem needs correct notification and promulgation.

It is recommended that;

4.1  IFATCA Provisional Policy is:

When using ADS-B ITP, proper mitigation must be in place to account for misidentification by the pilot due to incorrect input of FlightID.

And is included on page 3 2 3 26 (new page) of the IFATCA Technical and Professional Manual.

4.2  That a study on the issue of incorrect FlightID is included in the 2009/10 Technical work programme.

ATSA-ITP Safety, Performance and Interoperability Requirements Document for ITP RTCA/DO-312.

Final Plenary discussions – SASP meeting WG/WHL/14.

ITP discussions at SASP WG/WHL/14.

SASP/WG/WHL/13 PT-6 Report Appendix E.

RTCA Paper No. 127-08/SC186-263 May 1, 2008 FORTY-FOURTH MEETING SC-186 AUTOMATIC DEPENDENT SURVEILLANCE – BROADCAST (ADS-B).

ITP Comment Presentation – SC186-WG51 Plenary 24-04-2008.